Representations of software architecture are an enabler for communication between all parties (stakeholders) interested in the development of a computer-based system. An architectural style defines as a family of such systems in terms of a ① of structural organization. More specifically, each ② describes a system category that encompasses: (1) a set of components (e.g., a database, computational modules) that perform a function required by a system, (2) a set of ③ that enable "communication, coordination and cooperation" among components, (3) ④ that define how components can be integrated to form the system, and (4) semantic models that enable a designer to understand the overall properties of a system by analyzing the known ⑤of its constituent parts.
①是（）
A. function
B. data flow
C. pattern
D. position level
